There are two major, and three minor, research projects under investigation in the Drosophila laboratory. (1) We are continuing to collect and analyze meiotic mutants with the aim of further articulating the genetic control of the meiosis-I-specific events of pairing, recombination and anaphase-I disjunction. Among other approaches: (a) we are looking for recombination-repair defective mutants by the criterion that they would be female-steriles made fertile by completely eliminating recombination (with c(3)G); (b) we are examining the effect of recombination-defective meiotic mutants on exchange in structurally aberrant chromosomes to determine what chromosome features are recognized by meiotic control signals; and (c) we are examining a meiotic mutant (mei-224) that is defective in a very early stage of meiosis (possibly the chromocenter) necessary for recombination, homologous segregation and distributive disjunction. (2) Having shown that two closely linked euchromatic autosomal mutants (da and abo) both produce maternal effects and both interact with (different) loci in the sex-chromosome heterochromatin, we are now examining the proposition that there is an autosomal region (31C-32C) containing a collection of regulators of heterochromatic genes that are most active during oogenesis. Aside from its intrinsic interest as a developmental process and the implication that perhaps linked genes are linked because they act at the same time in ontogeny, this system may allow a linear resolution of the X-chromosome heterochromatin. (3) Among the minor projects, are: (a) a continuing effort to make segmental aneuploids for chromosome regions not yet explored with the ultimate aim of exhibiting and mapping all dosage-sensitive loci in the Drosophila genome; (b) a continuing attempt to develop a biochemical phenotype of aging in Drosophila with the ultimate aim of finding aging mutants; and (c) further attempts to map and define the function of the components of the segregation-distortion system. Of particular interest is that we map the SD region, which is responsible for aberrant sperm-head condensation, near or at the histone loci, and histones are likely involved in normal spermiogenesis.